This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 28 049.8, filed on Jun. 6, 2000, the entire disclosure of which is incorporated herein by reference.
The invention relates to a method for controlling the weft insertion in a jet loom to achieve substantially identical weaving cycle times, and further relates to a jet loom for carrying out such a method.
German Patent 30 43 003 discloses a loom arrangement and a method for transporting the weft threads through the loom shed by means of a fluid jet. The basic object of the known method and apparatus is to operate the loom in an optimal manner by controlling the supply of high pressure fluid medium to the weft insertion nozzles during the weft insertion cycle, so that at every time point during the pick or weft insertion, just the right amount of high pressure fluid is provided to the insertion nozzles so that the desired weft insertion velocity or the desired weft insertion transit time is achieved in relation to the rotational speed of the loom. To achieve this, the known method provides for measuring the transport velocity of each inserted weft thread, then providing a signal representative of the measured transport velocity to a control system, which converts this signal to a control signal, which in turn influences or controls the pertinent components of the weft thread transport system for determining the travel velocity of the inserted weft thread.
More particularly, in a detailed embodiment of the known method and apparatus mentioned above, the time required for carrying out the weft transport, i.e. the weft flight time or weft transit time, is continuously measured, and then the average weft insertion time is determined over a plurality of successive picks or weft insertions. The determined average weft insertion time is compared to the desired weft insertion time, and then a signal representative of the determined time difference is provided to a control system in which this signal is converted into a control signal, which in turn influences the components of the weft thread transport system to adjust the weft insertion velocity for subsequent insertion cycles.
Thus, in order to form or obtain a control signal for influencing the components of the weft thread transport system, the known method calls for determining an average weft insertion time over a plurality of successive picks or weft insertions, with respect to each particular type of weft thread. Namely, each different weight, material, density, tightness, or surface characteristic of weft thread will generally have a different weft thread flight time or transit time for a given control condition of the weft insertion system. Thus, the average weft insertion time must be determined separately for each particular type of weft thread.
Then, the determined actual average weft insertion time is compared to the nominal weft insertion time for the respective associated weft thread type. That is a rather complicated and time consuming process and requires the loom operator to have at hand or to determine the necessary parameters of each type of weft thread that is to be processed by the loom.
The above mentioned German Patent 30 43 003 does not disclose any details regarding the type, arrangement and construction of the components of the weft thread transport system. Generally, however, it is known that weft thread transport systems in jet looms include insertion jet nozzles, a supply of pressurized fluid, and magnetic valves for switching, controlling or regulating the volume flows of the pressurized fluid to the respective nozzles.
In a different context, it is known to equip a valve with a piezoelectric drive or valve actuator, for example as disclosed in German Patent 197 23 388 or German Patent Laying-Open Publication 195 47 149. However, it is not known in the prior art to use such piezoelectrically actuated valves as components in a weft thread insertion system of a jet loom. Since the piezoelectrically actuated valves have different operating characteristics magnetically actuated valves, they would not be suggested as a simple replacement or exchange of the magnetic valves that are known in looms.
In view of the above, it is an object of the invention to provide a loom arrangement and a method for achieving substantially identical weaving cycle times while expressly avoiding the determination of an average weft insertion time per each respective weft thread type. It is a further object of the invention to provide a loom including a valve arrangement, as well as an operating method, which can compensate any time difference arising between the actual weft thread flight time and the nominal or rated weft thread flight time in a rapid reacting manner, substantially in real time on an on-going basis from cycle to cycle during operation of the loom. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a method of achieving substantially identical weaving cycle times and particularly weft insertion times for successive weft threads to be inserted into a loom shed of the loom by means of jet insertion nozzles, regardless whether the successive weft threads have identical thread quality parameters or respective differing thread quality parameters. The invention involves the following steps. Data representing at least one thread quality parameter of each weft thread that characterizes the weft thread flight time of this weft thread is stored in a data bank provided in the loom controller of the loom. A respective nominal or rated pressure profile or curve as a function of time that is intended to reliably ensure attainment of the desired nominal weft thread transit or flight time is allocated to the respective characteristic thread quality parameter. The actual thread flight time of each respective weft thread is measured and compared to the rated or nominal thread flight time. The just mentioned comparison results in a signal arising from the difference between the nominal thread flight time and the actual thread flight time, and this signal is delivered to the loom controller, in which the signal is converted into a control signal.
According to a first embodiment of the invention, this control signal is provided to a valve arrangement operatively connected to the weft thread insertion system, e.g. interposed between the pressurized fluid supply and the insertion nozzle or nozzles. Responsive to the control signal, this valve arrangement controls the pressure and/or the quantity of the pressurized fluid being provided to the insertion nozzles, in the sense of a continuous variation of the actual pressure profile of the pressurized fluid provided to the insertion nozzles. In effect, this is also a continuous adjustment of the nominal pressure profile. This can be carried out, for example, either by actually updating the previous stored nominal pressure profile data to a new revised nominal pressure profile to be used for subsequent weft insertions, or by superimposing the control signal over the previous or initial nominal pressure profile to provide a new revised nominal pressure profile signal based on a combination of the control signal and the previous or initial pressure profile.
According to a second embodiment of the inventive method, the control signal generated in the loom controller responsive to the difference between the nominal thread flight time and the actual thread flight time is used to control or adjust the rotational speed of the loom itself. Namely, in this embodiment, the signal resulting from the time difference between the actual thread flight time and the nominal thread flight time is used as a significant value for adapting the rotational speed of the main drive of the loom to the nominal thread flight time. In other words, rather than adjusting the pressure and/or the quantity of the pressurized fluid supplied to the weft insertion nozzles, the operating speed of the loom itself is adjusted.
The above objects have further been achieved in a jet loom with a particular inventive valve arrangement for carrying out the above described methods. According to the invention, the valve arrangement includes piezoelectric actuators for regulating or controlling the pressure and/or the quantity of the pressurized fluid being supplied to the weft insertion nozzles. Further, the valve arrangement comprises at least one frame-like valve module having a valve outlet, with a respective one of the piezoelectric actuators connected to a valve disk that acts on the valve outlet. The valve arrangement further comprises first and second head-side flange plates between which the valve module is (or valve modules are) received and secured. At least one of the flange plates has a valve inlet therein. The pressurized fluid thus enters the valve arrangement through the valve inlet in one of the flange plates, and then selectively passes through the valve arrangement to exit through the valve outlet, under the control of the valve disk being selectively moved by the piezoelectric actuator.
A plurality of these valve modules, each having the same construction, can be assembled together to form the overall modular valve arrangement, whereby each one of the modules includes its own separately controllable piezoelectric actuator. Each one of these piezoelectric actuators is, for example, embodied as a vibrating or oscillating element with one fixed end and one freely vibrating end, whereby the respective valve disk is mounted on the free end of the actuator and positioned opposite the valve outlet of the respective valve module. In this embodiment in which the overall valve structure includes plural individual valve modules, each one of the valve modules is respectively allocated to and connected to a single weft insertion nozzle or a group of weft insertion nozzles of the weft thread insertion system.
As described above, each valve module has its own respective valve outlet that is individually controllable as also described above. However, the overall valve structure including plural valve modules has at least one common valve inlet. This valve inlet is preferably provided in one of the head-side flange plates that terminates the overall valve arrangement, i.e. holds and seals the valve modules therebetween. In other words, a plurality of the frame-like valve modules can be stacked adjacent one another and then enclosed or sandwiched between the flange plates acting as end plates. Thereby, the inner valve space within each valve module adjoins and freely communicates with the inner space of all the other valve modules, which in common receive the incoming pressurized fluid through the at least one common valve inlet.
At least one sensor, which detects the static pressure prevailing within the overall valve structure, is arranged within at least one of the valve modules, i.e. within the common inner space of the overall valve structure. The detected pressure value is represented as a corresponding electrical signal which is transmitted in any signal transmission manner, e.g. via an electrical conductor, from the pressure sensor to the loom controller.
A further sensor can be integrated or arranged in the respective valve outlet of each valve module, to detect the dynamic pressure of the pressurized fluid (i.e. pressure medium) flowing from the respective valve outlet through a pressure line (e.g. a pressure hose, pipe, conduit, etc.) to a respective connected weft insertion nozzle or nozzle group. The detected pressure values are then transmitted in the form of electrical signals from this sensor to the loom controller. On the one hand, this sensor serves to monitor the dynamic pressure level in the respective associated weft insertion nozzle or nozzles. On the other hand, this sensor further provides feedback for compensating the difference resulting from the comparison between the nominal thread flight time and the actual thread flight time in the weft insertion, by correspondingly providing a changed pressure. Namely, by monitoring the dynamic pressure level, this sensor enables the loom controller to provide the appropriate control signals to vary or adjust the pressure or the through-flow quantity of the pressure medium through the respective valve module to the respective associated weft insertion nozzle or nozzles, so as to bring the actual weft flight time into conformance with the nominal weft flight time in a subsequent insertion cycle. This variation or adjustment corresponds to automatically establishing an altered new nominal pressure profile for the respective associated weft thread in a following weft insertion. Namely, once the best pressure profile for precisely achieving the desired nominal weft flight time has been attained, the dynamic pressure sensor provides a signal representing the actually measured pressure profile, which may then be used to establish an updated nominal pressure profile to be used for subsequent insertion cycles.
In a further detailed embodiment of the invention, each piezoelectric actuator can cooperate with a measuring system and/or a pre-tensioning or biasing arrangement, which respectively provides a prescribed default flow gap between the valve outlet and the valve disk, or to provide the complete closure of the valve outlet by means of the valve disk. In a first example, the pre-tensioning arrangement comprises a permanent magnet connected to the piezoelectric element, and cooperating with an electrical coil that can be energized by a d.c. current. In a second example, the pre-tensioning arrangement comprises a compression spring or a tension spring operatively connected to the piezoelectric element. In connection with any embodiment of the pre-tensioning arrangement, or even without such a pre-tensioning arrangement, the above mentioned measuring system can be any known path distance measuring system, position sensor, travel sensor, distance sensor, etc. for measuring the position of the piezoelectric actuator and particularly the valve disk relative to the valve opening.
The inventive method and apparatus achieve the advantage that a data bank already available in the loom controller of the jet loom can be utilized, with an expanded functionality, so that the characteristic quality parameter or parameters of a weft thread, which are stored in the existing data bank, are further associated with a nominal pressure profile for the weft insertion, which is defined by data that may also be stored in the data bank. The initial data for the nominal pressure profile is provided empirically or by prior testing results, whereby this initial nominal pressure profile is expected to achieve a desired nominal weft insertion thread flight time for a weft thread having the particular given associated thread quality parameter. The invention then further updates or overrides this initial nominal pressure profile with an altered new nominal pressure profile in the event the measured actual weft flight time diverges from the desired nominal weft flight time.
Through the inventive use of the above described valve structure, especially including fast-acting piezoelectric actuators, the nominal or rated pressure profiles can be continuously and automatically varied or newly established in such a manner so that an optimal nominal pressure profile is always given for the respective weft insertion. Particularly, by means of the automatic pressure regulation and adjustment, which is carried out continuously and automatically during a weft insertion process, any arising time differences between the nominal and actual values of the weft flight time, or especially time differences between successive weaving cycles, can be completely eliminated. Thereby, it is possible to achieve substantially identical weft insertion flight times and substantially identical weaving cycle times throughout a succession of weaving cycles, regardless of the thread type of the weft threads being inserted. A further advantage is that the pressure profiles can be automatically adapted to various rotational speeds of the loom, or viewed in the opposite manner, the rotational speeds of the main drive of the loom can be altered to be brought into correspondence with the nominal pressure profiles.
Using the new inventive valve structure, a more rapid reaction time is possible, in comparison to the previous conventional magnetic valves, and thereby the control dynamics during the weft insertion are improved. It becomes possible to automatically and adjust the pressure and/or supply volume of the pressure medium to the weft insertion nozzles in real time with very little delay. Thereby the weft acceleration, weft insertion speed, and the like can be very precisely and dynamically controlled. Moreover, in addition to the weft insertion itself through the main and relay nozzles, other auxiliary functions can also be controlled using the new valve structure, for example the flow of pressure medium can be controlled for achieving the threading-in of the weft thread into the main nozzle, as well as the pneumatic laying-in or tucking-in of the weft thread ends for forming a laid-in selvage. Additionally, the new valve structure can be located at any convenient position in or on the loom. That enables an optimum layout of the pressure hoses or the like.
At least for the main nozzle functions, the valve structure can be operated in a nearly wear-free manner, because a neutral or default non-zero valve opening can be prescribed for providing the required base weft thread holding air flow. Preferably, the valve structure is connected directly to, or arranged very close lo to the main nozzles or other pressure medium consumers, whereby a dead volume and associated dead time, which have previously been caused by the unavoidable pressure build-up time of the pressure medium in the pressure hoses, can be essentially avoided by the inventive arrangement. This in turn means that the invention achieves a direct delay-free (or at least a very short) reaction time and a high accuracy in achieving the control functions.
Since the overall valve arrangement is preferably only provided with a single common valve inlet, the operating reliability is improved and the maintenance requirements of the valve arrangement are simplified. Also, by appropriately dimensioning the valve modules, or even by adding so-called blind modules that do not provide an active valve outlet connection, the total internal volume of the overall valve structure can be increased to the required extent so that a separate reservoir tank for supplying air to the main nozzles can be omitted.